The subject matter disclosed herein relates to signal processing and, in one or more embodiments, to systems and methods to remove and/or filter acoustic energy from signals that monitor operation of valves in a process facility.
Valves in process facilities can exhibit various types of failure modes that can result in serious economic consequences and can pose a safety risk. Cavitation is one failure mode that occurs when the pressure drop across the valve causes the pressure of the working fluid to drop below the vapor pressure. This pressure drop causes gas bubbles to form. Collapse of these bubbles can damage the valve and piping. In another mode, the valve fails to close completely, which causes the working fluid to leak through the valve. Such leaks can indicate numerous problems with the valve. These problems may include damage to the components (e.g., the plug and/or the stem), the presence of debris that blocks and/or prevents full actuation of the plug, as well as failure of the actuator to provide enough force to fully close the valve.
Process facilities may employ several methods to detect these failure modes, as well as other problems with the valves. Examples of these methods often look for deviations in flow or pressure, e.g., downstream (and/or upstream) of the valve. In another example, the method monitors noise emitted by the valve. These methods are particularly useful because some mechanical failures (e.g., in the stem, the plug, the seat, and/or the valve actuator) may cause vibrations. Valves that are nearly closed often emit vibrations that indicate the presence of a leak in the valve. Detecting the acoustic energy of these vibrations and comparing the acoustic energy to the spectra of known leaking valves can help to detect the presence of leaks.
Although acoustic methods can detect leakage in pipelines, these methods are difficult to apply in a process plant because the valves in the process plant are subject to many acoustic sources that can interfere with the technique. Some methods overcome the problem with interference by restricting the detected frequency to the ultrasonic range. These frequencies are less influenced by energy that emanates from acoustic sources that are distant from the valve. Other methods measure ambient acoustic noise and directly subtract this measure from the signal that measures the acoustic energy at the valve. However, this method does not eliminate noise that can occur along the pipe. To further address the noise along the pipe, other methods have utilized multiple acoustic sensors; but, these methods have used the arrival times of the acoustic energy at the sensors to locate the “position” of the acoustic source in space rather than for the elimination of noise at the event.